As a method of heating a heating roller of a fixing apparatus, an example is known in which a heating member having an endless belt shape or a cylindrical (roller) shape is constituted of a heat-resistant film material including a metal layer (conductive film) having a small heat capacity, and brought into contact with a member to be fixed by use of induction heating.
An induction heating device passes a high-frequency current through a coil to generate electromagnetic waves, passes a current induced by the electromagnetic waves through the metal layer of the heating roller, and heats the heating roller by the Joule heat accompanying the induced current. When a frequency of the high-frequency current flowing through this coil is controlled, a surface temperature of the heating roller can be raised at a set temperature by the heating.
Such induction heating device has an advantage that it is possible to heat the heating roller in a short time. However, a high-precision temperature control is required in order to uniformly control the surface temperature of the heating roller in an axial direction. The coil is required to be held in a predetermined position with respect to the heating roller in order to achieve uniform magnetic characteristics of the metal layer of the heating roller and the coil in the axial direction.
However, there is a problem that when the high-frequency current is supplied to the coil, the coil vibrates a positional relation between the coil and the heating roller changes, and the magnetic characteristics change.
To solve the problem, as disclosed in Japanese Patent Application Laid-Open No. 2003-68442, a coil unit is known in which a coil holder 1 and a coil presser member 2 are manufactured by injection molding, next an electromagnetic induction coil 8 is attached to the coil holder 1, and the coil presser member 2 is bonded (fixed) to the holder. Moreover, the integrally bonded coil holder 1 and coil presser member 2, and the electromagnetic induction coil 8 are set into a mold for the injection molding to obtain a resin-sealing molded portion 3, thereby preventing the coil from being deformed or its position from being displaced.
However, in the coil unit disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2003-68442, the electromagnetic induction coil 8 is held by the coil holder 1 and coil presser member 2 as support members, and the molded portion 3 constituted by the resin-sealing molding. Therefore, since at least three types of molds are required for forming the coil holder member 1, the coil presser member 2, and the molded portion 3, respectively, a molding process becomes complicated, and this sometimes raises costs.
Moreover, when the coil is not securely held in a coil drawing portion, a lead wire of the coil comes into contact with the mold to break the coating of an electric wire, and the lead wire is sometimes disconnected.